Planar loudspeaker

ABSTRACT

The invention relates to a planar loudspeaker comprising a light, thin soundboard ( 2 ) which may be energized to produce multiply-reflected bending waves, a surrounding frame ( 3 ) holding the soundboard ( 2 ) in an articulated, shear-resistant manner; at least one driver ( 6, 7, 9, 10 ) connected to the soundboard ( 2 ) to energize the soundboard ( 2 ); and at least one bridge ( 13, 16, 18, 20, 22, 25 ), rigidly connecting the at least one driver ( 6, 7, 9, 10 ) to the frame ( 3 ), wherein the bridge or at least one of the bridges ( 13, 16, 18, 20, 22, 25 ) is connected to the damping board ( 14 ).

CLAIM OF PRIORITY.

This patent application claims priority to International ApplicationPCT/EP01/08104 filed on Jul. 13, 2001.

FIELD OF THE INVENTION.

This invention relates to the field of loudspeakers, and in particularto a planar loudspeaker comprising a light, thin soundboard that may beenergized to produce multiple-reflected bending waves. A surroundingframe holds this board in an articulated manner, At least one driver isconnected to and energizes the soundboard, and at least one bridgerigidly connects the at least one driver to the frame.

RELATED ART

U.S. Pat. No. 5,701,359 discloses a rigid-panel-type loudspeaker thatfunctions on the principle of a free piston, wherein the sound-radiatingsurface (e.g., a diaphragm) is rigid (e.g., like a piston). Thesound-radiating surface does not effect any significant flexuralvibrations in the operating frequency range, and the rigid panelprovided as the sound-radiating surface is free (i.e., open and notenclosed by a cabinet in an airtight manner).

WO 97/09842 discloses multiresonance loudspeakers, wherein weaklyattenuated bending waves occurring in the operating frequency range arereflected at the panel edges such that the diaphragm becomes amultiresonator in response to the formation of standing waves. Suchmultiresonance loudspeakers are also referred to as “multiresonancesoundboards”, “bending-wave loudspeakers” or “distributed modespeakers.” In multiresonance loudspeakers the panel is usually alsoindependent (i.e., not a component of a closed box).

The remaining types of electrodynamic panel drivers (see, for example,DE 199 409 30) may in principle be fixed to the panel in a floatingdesign (i.e., without being supported by a frame). The mass of themagnet system then forms the dynamic counter-support for the applicationof force to the panel to be driven (principle of “seismic mass”).

If the panel is driven in such a way that the panel normal is orientedapproximately vertically relative to gravity, then the heavy magnetsystems of the drivers apply gravitational force to the panel throughtheir crimps. Due to the low rigidity of the crimps, these undergo acreeping settling motion over time in response to gravity, therebycausing an eccentrically acting, irreversible misalignment of the voicecoils. Although a settling of this type also occurs even in horizontalassemblies, such as in cover panels, the settling direction here is notin an eccentric (radial) direction but in the direction of the voicecoil axis.

In order to prevent this destructive, eccentric creeping effect, thedrivers in vertically operating planar loudspeakers are attached toso-called “bridges” in such a way that their weight is unable to exertany shear force on the panel. These bridges (also referred to as“traverses,” or “gantries”) are attached to frames, which in turnsupport the panel by its rim in a shear-resistant articulated manner.

Due to their relatively large span, a bridge of this type usually actslike a flat spring that forms a low-damping, spring-mass vibrationalsystem. In the resonance frequency located in the bass range, thisvibrational system (bridge resonator) exerts strong deflections withoutradiating any noticeable sound. The strong deflections in bridgeresonance are able to overload the voice coil centering and ultimatelydestroy the driver.

Therefore, there is a need for a planar loudspeaker with protectionagainst settling in which the dynamic side-effects of this settlingprotection are avoided.

SUMMARY

A planar loudspeaker includes a bridge that is connected to a dampingboard. The bridge supports a driver and the damping board. The dampingboard is preferably rigid.

The bridge resonance frequency may be tuned here by, for example,adjusting mass. Specifically, the bridge resonance may be determined bythe ratio of the spring constant to the total bridge mass including allelements attached to it. Independently of the damping provided by theboard surface of the damping board, the mass may be modified by changingthe thickness or the density of the damping board in such a way that theradiative contribution of the damping board integrates in a positivemanner into the acoustic spectrum of the multiresonance loudspeaker.

In an example of an alternative approach, the bridge resonance frequencymay be tuned by adjusting the spring. Independent of the dampingprovided by the board surface, the planar moment of inertia, and thusthe spring constant, may, for example, be adjusted by modifying thecross-sectional profile of the bridge in such a way that the resonancezone of the bridge integrates in a positive manner into the acousticspectrum of the multiresonance loudspeaker.

In a preferred approach, at least one bridge is created in the form ofan air-permeable rigid frame. The at least one bridge may, however, alsobe created in the form of an airtight flat box cover.

The damping board preferably has a smaller area than the soundboard. Inaddition, a preferred approach implements the damping board using alight, extremely flexurally rigid sandwich construction. A sandwichconstruction of this type is known, for example, from EP 0 924 959.

In addition, the connection points between the bridge(s) and dampingboard may be located in the region of the node lines for the first twovibrational modes of the damping board. The damping board itself mayalso be an integral component of the at least one bridge.

The at least one bridge may be composed of a prismatic rod, wherein thebridge does not completely cover the area opposite the soundboardprovided by the frame. In addition, the at least one bridge may becreated in the form of a regular lattice and/or perforated panel.

In another modification of the invention, the at least one bridge may beelastically compliant and an integral component of an airtight flat boxin which all external components of this flat box are themselvesairtight, as well as interconnected in an airtight manner. The flat boxhere may have a bass reflex port (or also a bass reflex tube). At leastone bridge may be in the form of a rigid panel and be connected to thedamping board by a surrounding bridge crimp.

A chamber may also be attached to the flat box, wherein the chamber mayalso have a bass reflex port (or also a bass reflect tube).Alternatively, the chamber may also be airtight. In addition, thechamber may also have a passive radiator. In terms of its acousticeffect, the planar loudspeaker according to the invention may also be anasymmetric two-panel loudspeaker since the principal front soundboardfacing the listener forms an acoustic multiresonance soundboard, whilethe smaller rear damping board facing away from the listener is,acoustically speaking, a rigid panel.

The degree of damping here may be directly adjusted by the surface areaof the damping board. The larger the board, the greater the damping.Additional enhancement of the low-frequency sound radiation by theplanar loudspeaker may be achieved by designing the damping board as arigid panel, thereby not only damping the bridge resonance vibration butalso simultaneously contributing to sound radiation in the low-frequencyrange. In free multiresonance soundboards, the low-frequency range isalways degraded by a dipole short circuit. The additional soundradiation partially compensates this dipole short circuit.

A particular advantage of the asymmetrical two-panel loudspeaker relatesto its simple driving technology. Whereas known monopole drivers (see DE198 218 62) are composed of back-to-back single drivers, alternativeside-by-side single drivers, or complex double voice-coil systems, aloudspeaker according to an aspect of the invention requires only atleast one known conventional panel driver.

If the frame supporting the bridge(s) and soundboard is acousticallyopen, then in response to a counter-acting pumping motion of the twopanels, the compressed or decompressed air flows through the frameopenings so as to equalize the pressure. If alternatively, however, theframe is sealed such that the soundboard and damping board createradiative surfaces of an otherwise closed flat box, then the two panelswork in a counter-acting manner in the low-frequency range. Thearrangement of the two panels then forms a “low-frequency monopoleradiator,” that is, a breathing sphere with partially inactive zones.

A preferred embodiment of such a flat-box arrangement ventilates the boxin a controlled manner. To this end, one or more bass reflex ports areprovided through which the interior air is able to exit in phase so asto obtain an improvement in the bass response. The ventilation of theflat box simultaneously avoids the negative effect of excessively rigidair compliance.

In another preferred embodiment, the seal of the rigid damping board,located in the plane of the rear flat-box wall and originally notprovided to effect sound radiation, may be in the form of an extendedflat spring, thereby achieving an enlarged radiative surface along withan accompanying increase in radiative damping. This extended flat springdetunes the spring constant of the original bridge, a factor which mustbe considered during resonance tuning.

An advantage of the invention includes the fact that a settlingprotection that exhibits almost no damaging dynamic side-effects is ableto be realized with relatively little complexity and expense. Inaddition, the implementation according to the invention generates anadditional acoustic radiation in an otherwise inadequately provided bassfrequency range.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the following claims.

DESCRIPTION OF THE DRAWING

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is cross sectional illustration of a first embodiment of a planarloudspeaker in the form of a free, asymmetrical two-panel loudspeaker inwhich the damping board is attached to one bridge;

FIG. 2 is a cross sectional illustration of a second embodiment of aplanar loudspeaker in the form of a free, asymmetrical two-panelloudspeaker in which the damping board takes on part of the bridgefunction;

FIG. 3 is a cross sectional illustration of a third embodiment of aplanar loudspeaker in the form of a free, asymmetrical two-panelloudspeaker in which the bridge rods emulate a disk spring;

FIG. 4 is a cross sectional illustration of a fourth loudspeakerembodiment in the form of a closed, asymmetrical two-panel loudspeaker;

FIG. 5 is a cross sectional illustration of a fifth embodiment of aplanar loudspeaker in the form of a closed, asymmetrical two-panelloudspeaker with a bass reflex port;

FIG. 6 is a cross sectional illustration of a sixth embodiment of aplanar loudspeaker in the form of a closed, asymmetrical two-panelloudspeaker with a rigid panel bridge and bridge crimp; and

FIG. 7 is a cross sectional illustration of a seventh embodiment of aplanar loudspeaker in the form of a closed, asymmetrical two-panelloudspeaker with two chambers, as well as a rigid panel bridge, bridgecrimp, and bass reflex port.

DETAILED DESCRIPTION

FIG. 1 illustrates a first embodiment of a planar loudspeaker 1. Theloudspeaker is configured as a asymmetrical two-panel loudspeaker, thatincludes a multi-resonance soundboard 2 that provides a diaphragm. Thesoundboard 2 has a relatively low mass, high bending stiffness, lowbending-wave damping, and a self-supporting frame attachment. A rigid,usually surrounding frame 3 holds the soundboard 2 by a surroundingpanel support 4, which acts as a shear-resistant articulated joint. Abridge 5 in the form, for example, of a narrow prismatic rod isconnected laterally (or at the back) to the frame by a rigid connection8 to a magnet system 6 of a driver, and simultaneously at the endsopposite the magnet. This carries the static load of the magnet system6. A voice coil 7 passing through the annular gap of the magnet system 6is centered by an internal crimp 10 relative to the magnet system 6 andat the same time attached to the soundboard 2. An external crimp 9 holdsthe static load of the magnet system 6 during assembly of theloudspeaker. It also functions as a floating magnet attachment so as toallow horizontal operation. In a multi-resonance planar loudspeaker withessentially free support, the frame 3 and/or bridge 5 contain openings11 (gaps) that provide for pressure equalization of the otherwiseenclosed air.

The asymmetrical two-panel loudspeaker 1 also includes a damping board14 that is attached to the bridge 5 and opposite soundboard 2. The largeplanar surface of the damping board 14 is aligned in a plane roughlyparallel to the large planar surface of the soundboard 2.

FIG. 2 is a cross-sectional illustration of a second planar loudspeaker12 configured as a free, asymmetrical two-panel loudspeaker. A dampingboard 14 is attached directly to the magnet system 6. Relatively shortbridge rods 16 connect the damping board 14 to the frame 3. The dampingboard 14 represents a widened part of the bridge 15 formed from thebridge rods 16, and thus performs the function of the bridge 15 torelieve static load. The large planar surface of the damping board 14 isaligned in a plane roughly parallel to the orientation of the largeplanar surface of the soundboard 2. In terms of the remaining elements,the embodiment of FIG. 2 matches the embodiment shown in FIG. 1.

FIG. 3 is a cross sectional illustration of a third embodiment of aplanar loudspeaker 17 configured as a free, asymmetrical two-panelloudspeaker. In contrast to the embodiment of FIG. 2, in this embodimentthe bridge rods 16 have been replaced by a surrounding disk spring 18.The static function of the disk spring 18 is the same as that for therods 16 in FIG. 2—with a different resulting acoustic behavior, however.The soundboard 2 is shielded from the possible presence of a nearby wallof a building, thereby providing a helpful remedy against theundesirable “wall effect”.

FIG. 4 is a cross sectional illustration of a fourth loudspeakerembodiment configured as a asymmetrical two-panel loudspeaker 19.Notably, this embodiment is configured and arranged as a closed,asymmetrical two-panel loudspeaker. This embodiment is similar to theembodiment of FIG. 3, with the principal exception that this embodimentdoes not include the ventilation openings 11 of the embodiment of FIG.3. In addition, in the embodiment illustrated in FIG. 4, a rear cover20, which acts as a disk spring, does not have any pores or openings.The compliance produced by the rear cover 20 is significantly hardenedby the compressive elasticity of the enclosed air.

FIG. 5 is a cross-sectional illustration of a planar loudspeakerconfigured and arranged as an asymmetrical two-panel bass reflexloudspeaker 21. In contrast to the embodiment of FIG. 4, one bass reflextube 23 is inserted into an opening in the frame 3. This approachprovides an additional means, beyond the bridge resonance, of providinga tunable, low-frequency filling-in of the response spectrum.

FIG. 6 is a cross sectional illustration of an embodiment of a planarloudspeaker configured as a closed, asymmetrical two-panel loudspeaker24 with a rigid panel bridge 25 and a bridge crimp 26. The damping board14 is resonantly connected to the panel bridge 25 through the bridgecrimp 26. The panel bridge 25 is connected to the frame 3.

FIG. 7 is a cross sectional illustration of an embodiment of a planarloudspeaker configured as a closed, asymmetrical two-panel two-chamberloudspeaker 27. The embodiment illustrated in FIG. 7 is substantiallythe same as the embodiment illustrated in FIG. 6 with the principalexception that in this embodiment the loudspeaker 27 includes a secondchamber 28, in addition to the rigid panel bridge 25 and the bridgecrimp 26. The second chamber 28 includes a bass reflex tube 23. Thesecond chamber 28 here is added on to the rear side of two-paneltwo-chamber loudspeaker 27, in other words, to the side of two-paneltwo-chamber loudspeaker 27 including damping board 14.

Instead of using a bass reflex tube 23, the second chamber 28 may beclosed, or have a passive radiator 29.

The illustrations have been discussed with reference to functionalblocks identified as modules and components that are not intended torepresent discrete structures and may be combined or furthersub-divided. In addition, while various embodiments of the inventionhave been described, it will be apparent to those of ordinary skill inthe art that other embodiments and implementations are possible that arewithin the scope of this invention. Accordingly, the invention is notrestricted except in light of the attached claims and their equivalents.

1. A planar loudspeaker, comprising: a soundboard that creates reflectedbending waves when energized; a frame; a panel support that connects thesoundboard to the frame in an articulated shear-resistant manner; adriver that energizes the soundboard; a crimp that connects the driverto the soundboard; a bridge having first and second ends and an interiorside and an exterior side, where the driver is connected to the interiorside of the bridge, and the first and second ends connect to the frame;and a damping board connected to the exterior side of the bridge.
 2. Theplanar loudspeaker of claim 1, where the damping board is rigid.
 3. Theplanar loudspeaker of claim 1, where the bridge comprises anair-permeable rigid frame.
 4. The planar loudspeaker of claim 1, where asurface area of the damping board is smaller than a surface area of thesoundboard.
 5. The planar loudspeaker of claim 1, where the dampingboard comprises sandwich construction.
 6. The planar loudspeaker ofclaim 1, where a plurality of connection points between the bridge andthe damping board are located in a region of a plurality of node linesof first two vibrational modes of the damping board.
 7. The planarloudspeaker of claim 2, where the damping board comprises an integralcomponent of the bridge.